Medical balloons are well known in the medical field and are used, for example, in the deployment of implantable medical devices such as stents and stent grafts, for angioplasty procedures, for temporary vessel occlusion, in valve repair procedures and so on. Often, it is desirous to inflate the balloon to a high pressure, particularly to dilate or otherwise open a vessel, to deploy a medical device and so on. However, a standard medical balloon formed only of a layer of polymer material is liable to rupture, leading to an abortive procedure and possible loss of balloon wall material into the patient's vasculature. Balloon rupture can also occur in cases where the balloon is scraped across a sharp object, such as plaque or other stenosis material within the vessel, or on a part of the medical device deployed off of the balloon.
It is also advantageous in many instances to have a balloon of reliable inflated diameter, that is of a diameter which will not vary over a range of balloon operating pressures. However, the materials commonly used for medical balloons do generally exhibit some stretch as inflation pressure increases, leading to the balloon having a non-constant inflated diameter over a range of operating pressures.
Problems can also occur during angioplasty procedure, when the clinician increases the pressure in the balloon in order to try to break the stenosis. When the stenosis does eventually break, this can lead to rapid expansion of the balloon and risk of it expanding beyond the natural diameter of the vessel.
The risk of balloon rupture can be reduced or avoided by the use of a strengthening sleeve disposed around the balloon, which may usefully be made of woven or braided fibers. Strengthening sleeves of this type are generally considered to retain flexibility of the balloon particularly when this is folded and wrapped. Such flexibility is a characteristic which is important in maintaining trackability during endoluminal insertion of the medical balloon into a patient.
A problem occurs with such strengthening sleeves is that as a result of the braiding or weaving of the sleeve, there is still experienced some expansion of the strengthening sleeve during inflation of the balloon, which causes the balloon to exhibit some variation in its inflated diameter.
Some examples of prior art medical balloons are disclosed in US 2012/0277783, US 2011/0046654, US 2006/0085022, U.S. Pat. Nos. 5,201,706 and 6,156,254.